Organic light emitting devices (OLEDs) have attracted much attention at present in virtue of their advantages such as wide view angle, high contrast and fast response time. Moreover, OLEDs can operate at a low voltage and achieve multi-color images. Therefore, a lot of research on OLEDs has been carried out.
A basic structure for a monochrome OLED comprises an anode, a cathode, and a light emitting layer arranged between the anode and the cathode. When a current is applied to the anode and the cathode on respective sides of the light emitting layer, electrons and holes will be recombined in the light emitting layer, thereby emitting light. Generally, by doping a host material of the light emitting layer with different dopants (hereinafter also referred to as guest materials) emitting light of different colors, an OLED emitting light of different colors can be produced.
In most existing approaches, OLEDs emitting blue light use a single-doped system. In other words, the organic light emitting layer comprises only one guest material emitting blue light. However, such a blue light OLED has many problems such as short service life and low light emitting efficiency.